1. Do NOT write shaders in Python everything except from def Output(**kwrgs) : return cd.p will be fricking ** _ _** ** slow**. I have written a noise shader and a uv-grid shader and both are sooooo slow.

2.Not sure what you mean by real-time. You can reload a shader plugin like every other python plugin. In some scenarios you will have to reassign the shader to the material, but if you just change moo = 5+i to moo = i^5 you can reload and rerender without any further steps.

3. I am not aware of any access to these features in python, I would be surprised if it is the case. But on the other hand I am often surprised ;)

I might have misunderstood your posting a bit, as the topic is "testing of shaders". For testing
python is fine or actually perfect. I did fixate a bit on your seemingly performance related question
regarding embree and pr.

so long story short : testing some sort of shader code - good idea, expecting anything close to
the usual shader performance or even production ready - won't happen.